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Strategy

Opportunities to exchange different kinds of pieces come up all the time in a game of chess. To determine whether or not a given exchange is favorable, the following system is widely used. A pawn is given a value of 1 point, and the other pieces are given values in terms of approximately how many pawns they are worth. These values are: knight 3, bishop 3, rook 5, queen 9. A king, of course, is priceless (its "combat" effectiveness, though, is a little better than a knight's).

In reality, piece values vary with the position and the stage of the game. The above values are fairly accurate for endgames, where a rook is generally equal to a minor piece and two pawns; but in the opening and middle game, a rook is worth only about a pawn more than a minor piece. Bishops are better than knights in most endgame positions and in middle games with open lines, while knights are superior in closed, blockaded positions or when all the pawns are on one side of the board. A knight supported by a pawn on an advanced outpost (fifth or sixth rank) from which it cannot be driven away by a pawn or other minor piece has a value close to that of a rook.

In the opening and middle game, center pawns are the most valuable and pawns on the edges the least valuable. A doubled pawn is worth less than two ordinary pawns, and often becomes a target for attack. A passed pawn has extra value, which increases dramatically the farther it advances: As a rule of thumb, when it is supported and safe from capture, a passed pawn is worth about a minor piece on the sixth rank and a rook on the seventh rank.

Material, or force, is only one measure of a player's assets in a position. Two other important measures are time and space.

In this position, White is a knight behind but is far ahead in development. White has gained several tempi over black--a tempo being a unit of time equal to one move. White has good prospects despite having one fewer piece.

In the following position, White has another kind of advantage: space. The black pieces have only two or three ranks on which to maneuver, while the white forces have four or five. This means more limited options for Black, and a more difficult position to play.

Force, time, and space can be converted into one another. A common tactic, for example, is to give up a pawn to gain time--that is, while the opponent spends two or three moves capturing the pawn and getting his piece that made the capture back to safety, a player may be able to move his or her pieces to better squares and build an attack.

Tactics

Throughout the game, players must be alert to the possibilities of combinations that win material or, occasionally, lead to checkmate. Forks and skewers are two of the most basic tactics; both involve attacks on two or more targets, not all of which can be defended. In the following diagram, for example, the White knight is forking the black king and queen, the White Queen is forking the bishop and knight, and the White bishop is skewering the two rooks.

Pins are another common tactic for winning material. A piece may be pinned against a king or against another piece. In the following position, Black's knight cannot move without putting the king in check. Even if Black defends the knight with d7-d6, White can win it by playing f2-f4.

Forks, skewers, and pins can often be brought about by making a temporary sacrifice.

In this position, Black has just moved the queen to g6 to threaten Qg6xg2 mate. This was a fatal mistake, however. White now plays Re1xe4, forcing Re8xe4, and now the Black rook is pinned against the queen by White's bishop. White now plays f2-f3, and Black will come out a piece behind.

Pieces can become overworked when they try to do two or more jobs at once. In the following position, Black has just blundered by moving a knight to h4.

The trouble is that Black's bishop on f6 is tied down to the defense of g7. If the bishop stops defending g7, White can play Qg2xg7 mate. Therefore, the Black bishop is not really defending the knight on h4, and White wins a piece by playing Nf3xh4.

The following position shows two other standard themes, deflection and back-rank weakness. Black seems to have an equal position at first glance, but White wins by playing Re1-e8+. The only way out of check is Rd8xe8, after which White plays Qd3xd5 and has an easily won game.

Players must be wary of the possibility of interpolations, or zwichenzugs-- moves made prior to answering a threat, and which must be answered. In the following position, White has just played Nc3-d5. If Black plays Qa5xd2, White will not recapture the queen immediately, but instead will play Nd5xe7+. After Kg8-h8, Rd1xd2, White has won a pawn. (To avoid this, Black had to retreat the queen to d8.)

A common kind of interpolation is one in which an attacked piece gets away by giving check or attacking another piece. Before answering an opponent's attack on one of your pieces by attacking one of his or her pieces, be sure the piece you're attacking cannot make a new attack, leaving you with two pieces hanging. Of course, if your piece the opponent is attacking can itself give check ... well, it can get complicated (that's chess).

Openings

In the opening and for most of the game, players should attempt to control the four center squares, as well as the 12 squares around them. On an empty board, bishops, knights, and queens attack more squares when on a center square than when they are near the edge. It's equally important to get your own pieces to these good squares and to keep the opponent from doing the same. In most openings, each player will initially take control of the two center squares of one color. For example, after 1.d2-d4, d7-d5, White temporarily has control of the dark squares, while Black has control of the light squares. The move 2.c2-c4 then challenges Black's light-square grip. Whether Black now takes the pawn or defends with e7-e6 (either move is good), Black must give a high priority to advancing a pawn to either c5 or e5. Other things being equal, if White is able to prevent Black from playing either of these moves, White will have a strategically won game.

The most common opening moves for White are 1.e2-e4 (King's Pawn Ending) and 1.d2-d4 (queen's pawn opening). Also popular are 1.c2-c4 (English Opening) and 1.Ng1-f3 (which most often transposes into positions similar to queen's pawn or English openings).

In all openings, players aim to develop their pieces quickly and efficiently, on squares where they control the center or disrupt opposing control of the center. Usually both players will castle at an early stage, connecting their rooks, and then bring their rooks to bear on open or half-open files.

Generally it's best to move least valuable pieces out first, most valuable pieces last. The queen should not be moved out early, as it presents a target for the opponent to attack. If you are forced to move your queen repeatedly while your opponent develops several pieces, you will be in trouble.

Noncommittal moves should be made before committal moves. For this reason, the first nonpawn move should usually be with a knight, for which the best square is the easiest to determine. For example, when it's clear that your king's knight's best development will be to f3 (or occasionally e2), chances are you'll still be considering several possibilities for your king's bishop. By first making the move you know you are going to make, you can then take your opponent's next move into account when you move your bishop.

Don't move the same piece more than once without a good reason. Move one pawn to open a line for each bishop, but don't move many other pawns until your pieces are developed. Above all, fight for control of the center, as discussed above. If the opponent has advanced pawns to the fourth rank in two of the four central files, you must do the same to keep your share of center control.

Here are just a few samples of frequently played openings. Analyses of thousands of different opening variations can be found in numerous chess books, periodicals, and software.

The Ruy Lopez

Sicilian Defense (Dragon Variation)

Queen's Gambit Declined

King's Indian Defense

Middle Game

After most pieces have been developed, the game enters the middle game. Players should continually try to improve their position by taking control of open lines, attacking important center squares or squares near the opponent's king, and bringing their pieces to squares where they are most effective.

When your pieces have reached their ideal squares, and not before, it's time to move a pawn.

Every pawn move, even good moves like the advance of a center pawn in the opening, permanently weakens the squares that the pawn had previously defended. Unlike piece moves, pawn moves cannot be undone because pawns cannot move backward. It's especially dangerous to advance the pawns in front of your king's castled position. While it's common and reasonably safe to castle on a side where a bishop is fianchettoed, or where the edge pawn has advanced one square, a castle in which no pawn has moved is the most secure. Pawn moves around the castle should only be made when absolutely necessary.

Pawns can be advanced to drive enemy pieces from their best squares, to open lines of attack, and to exchange opposing pawns that are shielding the king or other pieces from attack. As pawns are moved and exchanged, players should try to keep their pawn structure as strong as possible. That means avoiding doubled pawns, backward pawns, and the creation of holes--squares that a player can never attack with a pawn, and which the opponent is likely to exploit by occupying with a piece, especially a knight.

In the following position, White's doubled a pawns are easily restrained by Black's lone a pawn, and so are hardly worth more than one pawn. Black's e pawn is backward, unable to advance with the support of another pawn; and a result, Black has a hole at e6. If White can post a knight there that Black cannot exchange off, it will be at least as valuable as a rook.

Less serious a weakness than doubled pawns or holes are isolated pawns, such as Black's a and c pawns and White's e pawn (and doubled a pawns) in the previous diagram. If the opponent has an isolated pawn, a player should aim to restrain it (keep it from advancing), blockade it, and attack it. If you can keep the opponent's pieces busy defending a pawn, you'll have an advantage.

In the middle game, players should analyze the position as objectively as possible to determine each side's strengths and weaknesses, then form an plan that takes advantage of their own strengths and exploits the opponent's weaknesses. A player with an advantage should attack, or risk losing the advantage. A player with a disadvantage should think defensively; attacking from a position of weakness is an easy way to lose quickly.

After coming up with a plan, a player must focus on finding moves that will further that plan. At the same time, it pays to try to figure out the opponent's most likely plan and to make it hard for the opponent to execute it. Once a player has found two or more moves that look good, sometimes called "candidate moves", he or she should try to choose among them by analyzing the likely sequence of moves that will follow from each move. The player must then mentally compare the resulting hypothetical positions and pick the one that seems best. If this sounds hard, it's because it is, but remember: Your opponent has the same problem.

When in doubt, win material. Being a pawn ahead in the middle game is usually enough to win a game in theory (practice is another matter, since it's hard to play mistake-free) provided the other side does not have compensating advantages. Many things can compensate for the loss of a pawn, however: greater mobility, a better pawn structure, a safer king position, control of key lines or squares. It's much harder to compensate for the loss of two pawns, and extremely hard to make up for a lost piece.

Here are a few other principles of middle game play:

The stronger your control of the center, the safer it is to expose your king.

If your opponent attacks on a wing, counterattack in the center.

Overprotect key squares, such as vital center pawns. If one of your pieces or pawns is defended by one more piece than is necessary to protect it, then each defending piece is free to move away, which means many more options.

After deciding on your move, before making it, give the board a final glance as if looking at the position for the first time just to be sure you're not overlooking something major.

End Game

As positions simplify through the exchange of pieces and pawns, it becomes easier to look farther ahead. Nevertheless, endgame play can be very subtle and tricky.

In an endgame, an advantage of two or more pawns is usually enough to win routinely. With other things being equal, being a pawn ahead is usually enough to win when players have pawns on both sides of the board, but not enough when all pawns are on one side of the board.

In endings with only kings and pawns, a crucial factor is often who has the opposition. This is similar to the concept of "the move" in Checkers. If two kings lie along the same line--a rank, a file, or a diagonal--with an odd number of squares intervening, the player who just moved has the opposition. In the simplest ending, king and pawn vs. king, having the opposition can mean the difference between winning and drawing.

In this position, if it's White's turn, the game is a draw: 1.e6-e7+, Kd8-e8 4.Kd6-e6 stalemate. But if it's Black's turn in the diagram, White wins: 1. ... Kd8-e8 2.e6-e7, Ke8-f7 3.Kd6-d7 followed by 4.e7-e8Q.

Here are some basic endgame principles to remember:

When you are one or two pawns ahead, exchange pieces but not pawns.

When you are one or two pawns behind, exchange pawns but not pieces, and try to eliminate all pawns from one side of the board.

Advance passed pawns as rapidly as possible.

Place rooks behind passed pawns--whether the pawns are yours or your opponent's.

Endings in which players have bishops of opposite colors (one moving on light squares, the other on dark squares) are the hardest to win if you're one or two pawns ahead, and the easiest to draw if you're one or two pawns behind.

Endings with only kings and pawns are the easiest to win when you're a pawn ahead.